Principles of Human Anatomy and Physiology, 11e1 Chapter 4 The Tissue Level of Organization Lecture Outline

Principles of Human Anatomy and Physiology, 11e 1

Chapter 4

The Tissue Level of Organization

Lecture Outline


INTRODUCTION

• A tissue is a group of similar cells that usually have a similar embryological origin and are specialized for a particular function.

• The nature of the extracellular material that surrounds the connections between the cells that compose the tissue influence the structure and properties of a specific tissue.

• Pathologists, physicians who specialize in laboratory studies of cells and tissues, aid other physicians in making diagnoses; they also perform autopsies.


Chapter 4 The Tissue Level of Organization

• Histology– the study of tissues


TYPES OF TISSUES AND THEIR ORIGINS

Four principal types based on function and structure• Epithelial tissue

– covers body surfaces, lines hollow organs, body cavities, and ducts; and forms glands.

• Connective tissue – protects and supports the body and its organs, binds

organs together, stores energy reserves as fat, and provides immunity.

• Muscle tissue – is responsible for movement and generation of force.

• Nervous tissue – initiates and transmits action potentials (nerve impulses)

that help coordinate body activities.


Origin of Tissues

• Primary germ layers within the embryo– endoderm– mesoderm– Ectoderm

• Tissue derivations– epithelium from all 3 germ layers– connective tissue & muscle from mesoderm– nerve tissue from ectoderm– Table 29.1 provides a list of structures derived

from the primary germ layers.


DEVELOPMENT

• Normally, most cells within a tissue remain in place, anchored to– other cells– a basement membranes– connective tissues

• Exceptions include phagocytes and embryonic cells involved in differentiation and growth.


Biopsy

• Removal of living tissue for microscopic examination– surgery– needle biopsy

• Useful for diagnosis, especially cancer• Tissue preserved, sectioned and stained before microscopic

viewing


CELL JUNCTIONS

• Cell junctions are points of contact between adjacent plasma membranes.

• Depending on their structure, cell junctions may serve one of three functions.– Some cell junctions form fluid-tight seals between cells.– Other cell junctions anchor cells together or to

extracellular material.– Still others act as channels, which allow ions and

molecules to pass from cell to cell within a tissue.


CELL JUNCTIONS

• The five most important kinds of cell junctions are tight junctions, adherens junctions, desmosomes, hemidesmosomes, and gap junctions (Figure 4.1)


Cell Junctions

• Tight junctions

• Adherens junctions

• Gap junctions

• Desmosomes

• Hemidesmosomes


Tight Junctions

• Watertight seal between cells• Plasma membranes fused with

a strip of proteins• Common between cells that line

GI and bladder


Adherens Junctions

• Holds epithelial cells together• Structural components

– plaque = dense layer of proteins inside the cell membrane

– microfilaments extend into cytoplasm

– integral membrane proteins connect to membrane of other cell


Gap Junctions

• Tiny space between plasma membranes of 2 cells

• Crossed by protein channels called connexons forming fluid filled tunnels

• Cell communication with ions & small molecules

• Muscle and nerve impulses spread from cell to cell– heart and smooth muscle of gut


Desmosomes

• Resists cellular separation and cell disruption

• Similar structure to adherens junction except intracellular intermediate filaments cross cytoplasm of cell

• Cellular support of cardiac muscle


Hemidesmosomes

• Half a desmosome• Connect cells to extracellular

material– basement membrane


EPITHELIAL TISSUES


Epithelial Tissue -- General Features

• Closely packed cells with little extracellular material– Many cell junctions often provide secure attachment.

• Cells sit on basement membrane– Apical (upper) free surface– Basal surface against basement membrane

• Avascular---without blood vessels– nutrients and wast must move by diffusion

• Good nerve supply• Rapid cell division (high mitotic rate)• Functions

– protection, filtration, lubrication, secretion, digestion, absorption, transportation, excretion, sensory reception, and reproduction.


Basement Membrane

• Basal lamina– from epithelial cells– collagen fibers

• Reticular lamina– secreted by connective tissue cells– reticular fibers

• Functions:– guide for cell migration during

development– may become thickened due to

increased collagen and laminin production

• Example: In diabetes mellitus, the basement membrane of small blood vessels, especially those in the retina and kidney, thickens.


Types of Epithelium

• Covering and lining epithelium– epidermis of skin– lining of blood vessels and ducts– lining respiratory, reproductive, urinary & GI tract

• Glandular epithelium– secreting portion of glands– thyroid, adrenal, and sweat glands


Classification of Epithelium

• Classified by arrangement of cells into layers– simple = one cell layer thick– stratified = two or more cell layers thick– pseudostratified = cells contact BM but all cells don’t

reach apical surface• nuclei are located at multiple levels so it looks

multilayered• Classified by shape of surface cells (Table 4.1)

– squamous =flat– cuboidal = cube-shaped– columnar = tall column– transitional = shape varies with tissue stretching


Epithelium


Simple Epithelium

• Simple squamous epithelium consists of a single layer of flat, scale-like cells (Table 4.1A)– adapted for diffusion and filtration (found in lungs and

kidneys)– Endothelium lines the heart and blood vessels.– Mesothelium lines the thoracic and abdominopelvic

cavities and covers the organs within them.• Simple cuboidal epithelium consists of a simple layer of

cube-shaped cells – adapted for secretion and absorption (Table 4.1B).


Simple Epithelium

• Simple columnar epithelium consists of a single layer of rectangular cells and can exist in two forms– Nonciliated simple columnar epithelium contains

microvilli (Figure 3.2)• increase surface are and the rate of absorption• goblet cells secrete mucus (Table 4.1C)

– Ciliated simple columnar epithelium contains cells with hair-like processes called cilia (Table 4.1D)

• provides motility and helps to move fluids or particles along a surface


Simple Squamous Epithelium

• Single layer of flat cells– very thin --- controls diffusion, osmosis and filtration

• blood vessel lining (endothelium) and lining of body cavities (mesothelium)

– nuclei are centrally located– Cells are in direct contact with each other.


Examples of Simple Squamous

• Section of intestinal showing serosa

• Surface view of lining of peritoneal cavity


Simple Cuboidal Epithelium

• Single layer of cube-shaped cells viewed from the side– nuclei are round and centrally located– lines tubes of kidney– adapted for absorption or secretion


Example of Simple Cuboidal

• X-Sectional view of kidney tubules


Nonciliated Simple Columnar

• Single layer rectangular cells• Unicellular glands (goblet cells) secrete mucus

– lubricate GI, respiratory, reproductive and urinary systems• Microvilli (non-motile, fingerlike membrane projections)

– adapted for absorption in GI tract (stomach to rectum)


Ex. Nonciliated Simple Columnar

• Section from small intestine


Ciliated Simple Columnar Epithelium

• Single layer rectangular cells with cilia• Unicellular glands (goblet cells) secrete mucus• Cilia (motile membrane extensions) move mucous

– found in respiratory system and in uterine tubes


Ex. Ciliated Simple Columnar

• Section of uterine tube


Pseudostratified Epithelium

• Pseudostratified epithelium (Table 4.1E) appears to have several layers because the nuclei are at various levels.

• All cells are attached to the basement membrane but some do not reach the apical surface.

• In pseudostratified ciliated columnar epithelium, the cells that reach the surface either secrete mucus (goblet cells) or bear cilia that sweep away mucus and trapped foreign particles.

• Pseudostratified nonciliated columnar epithelium contains no cilia or goblet cells.


• Single cell layer of cells of variable height– Nuclei are located at varying depths (appear layered.)– Found in respiratory system, male urethra & epididymis

Pseudostratified Ciliated Columnar Epithelium


Stratified Epithelium

• Epithelia have at least two layers of cells.– more durable and protective– name depends on the shape of the surface (apical) cells

• Stratified squamous epithelium consists of several layers of– top layer of cells is flat– deeper layers of cells vary cuboidal to columnar (Table

4.1F).– basal cells replicate by mitosis

• Keratinized stratified squamous epithelium– a tough layer of keratin (a protein resistant to friction and

repels bacteria) is deposited in the surface cells. • Nonkeratinized epithelium remains moist.


Stratified Epithelium

• Stratified cuboidal epithelium (Table 4.1G) – rare tissue consisting of two or more layers of cube-shaped

cells whose function is mainly protective.• Stratified columnar epithelium (Table 4.1H) consists of layers of

cells – top layer is columnar– somewhat rare– adapted for protection and secretion

• Transitional epithelium (Table 4.1I) consists of several layers of variable shape.– capable of stretching / permits distention of an organ– lines the urinary bladder– lines portions of the ureters and the urethra.


Stratified Squamous Epithelium

• Several cell layers thick– flat surface cells– Keratinized = surface cells dead and filled with keratin

• skin (epidermis)– Nonkeratinized = no keratin in moist living cells at surface

• mouth, vagina


Papanicolaou Smear (Pap smear)

• Collect sloughed off cells of uterus and vaginal walls• Detect cellular changes (precancerous cells)• Recommended annually for women over 18 or if

sexually active


Stratified Cuboidal Epithelium

• Multilayered• Surface cells cuboidal

– rare – sweat gland ducts– male urethra


Stratified Columnar Epithelium

• Multilayered

– columnar surface cells

– rare

– very large ducts

– part of male urethra


• Multilayered – surface cells varying in shape

• round to flat (if stretched)– lines hollow organs that expand from within (urinary

bladder)

Transitional Epithelium


Glandular Epithelium

• gland:– a single cell or a mass of epithelial cells adapted for

secretion– derived from epithelial cells that sank below the surface

during development

• Endocrine glands are ductless (Table 4.2A).• Exocrine glands secrete their products into ducts that empty

at the surface of covering and lining epithelium or directly onto a free surface (Table 4.2B).


Glandular Epithelium

• Exocrine glands– cells that secrete---sweat, ear wax, saliva, digestive

enzymes onto free surface of epithelial layer– connected to the surface by tubes (ducts)– unicellular glands or multicellular glands

• Endocrine glands– secrete hormones into the bloodstream– hormones help maintain homeostasis


Simple Cuboidal Epithelium


Structural Classification of Exocrine Glands

• Unicellular (single-celled) glands– goblet cells

• Multicellular glands– branched (compound) or unbranched (simple)– tubular or acinar (flask-like) shape


Examples of Simple Glands

• Unbranched ducts = simple glands• Duct areas are blue


Examples of Compound Glands

• Which is acinar? Which is tubular?


Duct of Multicellular Glands

• Sweat gland duct• Stratified cuboidal epithelium


Exocrine Glands – Functional Classification• Merocrine glands

– form the secretory products and discharge it by exocytosis (Figure 4.5a).

• Apocrine glands – accumulate secretary products at the apical surface of the

secreting cell; that portion then pinches off from the rest of the cell to form the secretion with the remaining part of the cell repairing itself and repeating the process (Figure 4.5b).

• Holocrine glands – accumulate the secretory product in the cytosol– cell dies and its products are discharged– the discharged cell being replaced by a new one (Figure

4.5c).


• Merocrine -- most glands– saliva, digestive enzymes &

watery (sudoriferous) sweat• Apocrine

– smelly sweat• Holocrine -- oil gland

– cells die & rupture to release products

Methods of Glandular Secretion


CONNECTIVE TISSUE

• abundant and widely distributed• derived from mesoderm• derived from mesenchyme

– Immature cells have names that end in -blast( e.g., fibroblast, chondroblast)

– Mature cells have names that end in -cyte (e.g., osteocyte).


Connective Tissues

• Cells rarely touch due to “extracellular matrix.”• Matrix (fibers & ground substance) is secreted by cells• Consistency varies

– liquid, gel or solid• Good nerve & blood supply except in cartilage & tendons


Connective Tissue Cells (Figure 4.6)

– Fibroblasts (which secrete fibers and matrix)– Adipocytes (or fat cells, which store energy in the form of

fat)– White blood cells (or leukocytes)

• Macrophages develop from monocytes– engulf bacteria & debris by phagocytosis

• Plasma cells develop from B lymphocytes– produce antibodies that fight against foreign

substances• Mast cells produce histamine that dilate small BV


Extracellular Matrix: Ground Substance

• Ground Substance– glycosamino glycans (GAG’s) hyaluronic acid,

chondroitin sulfate, dermatan sulfate, and keratan sulfate• hyaluronic acid is thick, viscous and slippery• chondroitin sulfate is jellylike substance providing

support• adhesion proteins (fibronectin) binds collagen fibers to

ground substance

• Chondroitin sulfate and glucosamine are used as nutritional supplements to maintain joint cartilage. It is not known why the supplements benefit some individuals and not others.


Extracellular Matrix: Fibers (Figure 4.6).

• Collagen fibers– composed of the protein collagen– tough and resistant to stretching– allow some flexibility in tissue– bone, cartilage, tendons, and ligaments.

• Elastic fibers– composed of the protein elastin surrounded by the glycoprotein fibrillin– provide strength and stretching capacity– skin, blood vessels, and lungs.

• Reticular fibers– composed of collagen and glycoprotein– support in the walls of blood vessels, in spleen, in lymph nodes– supporting network around fat cells, nerve fibers, and skeletal and

smooth muscle fibers.


Clinical Application: Marfan Syndrome

• Inherited disorder of fibrillin gene• Abnormal development of elastic fibers

– Tendency to be tall with very long legs, arms, fingers and toes

– Life-threatening weakening of aorta may lead to rupture


Embryonic Connective Tissue

• Connective tissue that is present primarily in the embryo or fetus is called embryonic connective tissue.

• Mesenchyme, found almost exclusively in the embryo, is the tissue form from which all other connective tissue eventually arises. (Table 4.3A)

• Mucous connective tissue (Wharton’s jelly) is found in the umbilical cord of the fetus.(Table 4.3B)


Embryonic Connective Tissue:Mesenchyme

• Irregularly shaped cells • semifluid ground substance with reticular fibers


• Star-shaped cells in jelly-like ground substance• Found only in umbilical cord

Embryonic Connective Tissue:Mucous Connective Tissue


Types of Mature Connective Tissue

• connective tissue proper– loose connective tissue

• consists of all three types of fibers, several types of cells, and a semi-fluid ground substance

– dense connective tissue• Cartilage

– Hyaline, elastic, reticular• bone tissue

– compact and trabecular• Blood and Lymph


Loose Connective Tissues

• Loosely woven fibers throughout tissues• Sub-types of loose connective tissue

– areolar connective tissue– adipose tissue– reticular tissue


Areolar Connective Tissue (Table 4.4A)

• Cell types = fibroblasts, plasma cells, macrophages, mast cells and a few white blood cells

• All 3 types of fibers present• Gelatinous ground substance• It is found in the subcutaneous layer of the integument


Areolar Connective Tissue

• Black = elastic fibers,• Tan/Pink = collagen fibers• Nuclei are mostly fibroblasts


Adipose

• Adipose tissue consists of adipocytes which are specialized for storage of triglycerides. (Table 4.4B)– found wherever areolar connective tissue is located.– reduces heat loss through the skin, serves as an energy

reserve, supports, protects, and generates considerable heat to help maintain proper body temperature in newborns (brown fat).

• Liposuction involves sucking out small amounts of adipose tissue.


Adipose Tissue

• Peripheral nuclei due to large fat storage droplet• Deeper layer of skin, organ padding, yellow marrow• Brown fat (found in infants) has more blood vessels and mitochondria

and is responsible for heat generation


Reticular Connective Tissue

• Reticular connective tissue consists of fine interlacing reticular fibers and reticular cells (Table 4.4C). – forms the stroma of certain organs.– helps to bind together the cells of smooth muscle.


Reticular Connective Tissue

• Network of fibers & cells that produce framework of organ• Holds organ together (liver, spleen, lymph nodes, bone marrow)


Dense Connective Tissue

Dense connective tissue contains more numerous, thicker, and dense fibers but considerably fewer cells than loose connective tissue.

Types of dense connective tissue– dense regular connective tissue– dense irregular connective tissue– elastic connective tissue


Dense Regular Connective Tissue

• Collagen fibers in parallel bundles with fibroblasts between bundles of collagen fibers

• White, tough and pliable when unstained (forms tendons)• Also known as white fibrous connective tissue


Dense irregular connective tissue

• Dense irregular connective tissue contains collagen fibers that are irregularly arranged and is found in parts of the body where tensions are exerted in various directions (Table 4.4E).– occurs in sheets, such as the dermis of the skin.– found in heart valves, the perichondrium, the tissue

surrounding cartilage, and the periosteum.


Dense Irregular Connective Tissue

• Collagen fibers are irregularly arranged (interwoven)• Tissue can resist tension from any direction• Very tough tissue -- white of eyeball, dermis of skin


Elastic Connective Tissue (Table 4.4F).

• Branching elastic fibers and fibroblasts• Can stretch & still return to original shape• Lung tissue, vocal cords, ligament between vertebrae


Cartilage

• Cartilage consists of a dense network of collagen fibers and elastic fibers embedded in chondroitin sulfate.– strength is due to its collagen fibers– resilience is due to the chondroitin sulfate– Chondrocytes occur with spaces called lacunae in the

matrix.• It is surrounded by a dense irregular connective tissue

membrane called the perichondrium.• Unlike other connective tissues, cartilage has no blood

vessels or nerves (except in the perichondrium).


Cartilage

• The growth of cartilage is accomplished by interstitial growth (expansion from within) and appositional growth (from the outside).

• Types of cartilage– hyaline cartilage– fibrocartilage– elastic cartilage


Three types of cartilage.

• Hyaline cartilage (Table 4.4G)– most abundant, but weakest– has fine collagen fibers embedded in a gel-type matrix– affords flexibility and support and– at joints, reduces friction and absorbs shock

• Fibrocartilage (Table 4.4H) – contains bundles of collagen fibers in its matrix– lacks perichondrium– strongest of the three types of cartilage

• Elastic cartilage (Table 4.4J)– contains a threadlike network of elastic fibers– perichondrium is present– provides strength and elasticity– maintains the shape of certain organs


Hyaline Cartilage

• Bluish-shiny white rubbery substance

• Chondrocytes sit in spaces called lacunae

• No blood vessels or nerves so repair is very slow

• Reduces friction at joints as articular cartilage


Fibrocartilage

• Many more collagen fibers causes rigidity & stiffness• Strongest type of cartilage (intervertebral discs)


Elastic Cartilage

• Elastic fibers help maintain shape after deformations• Ear, nose, vocal cartilages


Growth & Repair of Cartilage

• Grows and repairs slowly because it is avascular• Interstitial growth

– chondrocytes divide and form new matrix– occurs in childhood and adolescence

• Appositional growth– chondroblasts secrete matrix onto surface– produces increase in width


• Protects, provides for movement, stores minerals, site of blood cell formation

• Bone (osseous tissue) consists of a matrix containing mineral salts and collagenous fibers and cells called osteocytes.– Spongy bone

• sponge-like with spaces and trabeculae• trabeculae = struts of bone surrounded by red

bone marrow• no osteons (cellular organization)

– Compact bone (Table 4.4J)• solid, dense bone• basic unit of structure is osteon (haversian

system)

Bone (Osseous) Tissue


Compact Bone: Osteon (Haversion System)

• lamellae (rings) of mineralized matrix– calcium & phosphate---give it its hardness– interwoven collagen fibers provide strength

• Lacunae are small spaces between lamellae that contain mature bone cells called osteocytes.

• Canaliculi are minute canals containing processes of osteocytes that provide routes for nutrient and waste transport.

• A central (Haversian) canal contains blood vessels and nerves.


Liquid connective tissue

• Blood– liquid matrix called plasma– formed elements (Table 4.4K)

• Lymph is interstitial fluid flowing in lymph vessels. – Contains less protein than plasma– Move cells and substances (eg., lipids) from one part of

the body to another


• Connective tissue with a liquid matrix (the plasma)• Cell types include red blood cells (erythrocytes), white blood

cells (leukocytes) and cell fragments called platelets– clotting, immune functions, transport of O2 and CO2

Blood


MEMBRANES

Membranes are flat sheets of pliable tissue that cover or line a part of the body.

• Epithelial membranes consist of an epithelial layer and an underlying connective tissue layer (lamina propria)– include mucous membranes, serous membranes, and

the cutaneous membrane or skin.

• Synovial membranes line joints and contain only connective tissue.


Mucous Membranes

• Mucous membranes (mucosae) line cavities that open to the exterior (Figure 4.7a).– mouth, stomach, vagina, urethra, etc

• Epithelial cells form a barrier to microbes• The connective tissue layer of a mucous membrane is

called the lamina propria.• Tight junctions between cells prevent simple diffusion of

most substances.• Mucous is secreted from underlying glands to keep

surface moist


Mucous Membranes


Serous Membranes

• Simple squamous cells overlying loose CT layer– consist of parietal and visceral layers

• Squamous cells secrete slippery fluid• Lines a body cavity that does not open to the outside such as chest or

abdominal cavity• Examples:

– pleura, peritoneum and pericardium• membrane on walls of cavity = parietal layer• membrane over organs in cavity = visceral layer

• Serous membranes may become inflamed with the buildup of serous fluid resulting in pleurisy, peritonitis, or pericarditis.


Serous Membranes


Cutaneous Membranes

• Cutaneous membranes cover body surfaces and consist of epidermis and dermis (Figure 4.7c)


Synovial Membranes

• Line joint cavities of all freely movable joints• Line bursae, and tendon sheaths• No epithelial cells---just special cells that secrete slippery

synovial fluid (Figure 4.7d).


MUSCLE TISSUE• consists of fibers (cells) that are modified for contraction

(provide motion, maintenance of posture, and heat.)• three types.

– Skeletal muscle tissue is attached to bones, is striated, and is voluntary (Table 4.5A).

– Cardiac muscle tissue forms most of the heart wall, is striated, and is usually involuntary (Table 4.5B).

– Smooth (visceral) muscle tissue is found in the walls of hollow internal structures (blood vessels and viscera), is nonstriated, and is usually involuntary. It provides motion (e.g., constriction of blood vessels and airways, propulsion of foods through the gastrointestinal tract, and contraction of the urinary bladder and gallbadder) (Table 4.5C).


Skeletal Muscle

• Cells are long cylinders with many peripheral nuclei• Visible light and dark banding (looks striated)• Voluntary (conscious control)


Cardiac Muscle

• Cells are branched cylinders with one central nuclei• Involuntary and striated• Attached to and communicate with each other by intercalated discs

and desmosomes


Smooth Muscle

• Spindle shaped cells with a single central nuclei • Walls of hollow organs (blood vessels, GI tract, bladder)• Involuntary and nonstriated


NERVOUS TISSUE

• The nervous system is composed of only two principal kinds of cells: – neurons (nerve cells)– neuroglia (protective and supporting cells) (Table 4.6).

• Most neurons consist of a cell body and two types of processes called dendrites and axons.

• Neurons are sensitive to stimuli, convert stimuli into nerve impulses, and conduct nerve impulses to other neurons, muscle fibers, or glands.

• Neuroglia protect and support neurons (see Table 12.1) and are often the sites of tumors of the nervous system.


Nerve Tissue

• Cell types -- nerve cells and neuroglial (supporting) cells• Nerve cell structure

– nucleus & long cell processes conduct nerve signals• dendrite(s) --- signal travels toward the cell body • axon ---- signal travels away from cell body


EXCITABLE CELLS

• Neurons and muscle fibers are excitable cells – they show electrical excitability (action potentials).

• Action potentials will be discussed further in Chapters 10 and 12.


TISSUE REPAIR: RESTORE HOMEOSTASIS

• Tissue repair is the process that replaces worn out, damaged, or dead cells.

• Each of the four classes of tissues has a different capacity to replenish its parenchymal cells.– Epithelial cells are replaced by the division of stem cells

or by division of undifferentiated cells.– Some connective tissues such as bone has a continuous

capacity for renewal whereas cartilage replenishes cells less readily.

– Muscle cells have a poor capacity for renewal.– Nervous tissue has the poorest capacity for renewal


Tissue Repair: Restoring Homeostasis

• Worn-out, damaged tissue must be replaced• Fibrosis is the process of scar formation.

– If the injury is extensive granulation tissue (actively growing connective tissue) is formed.

• Adhesions, which sometimes result from scar tissue formation, cause abnormal joining of adjacent tissues, particularly in the abdomen and sites of previous surgery. These can cause problems such as intestinal obstruction.


Tissue Engineering

• New tissues grown in the laboratory (skin & cartilage)• Scaffolding of cartilage fibers is substrate for cell

growth in culture• Research in progress

– insulin-producing cells (pancreas)– dopamine-producing cells (brain)– bone, tendon, heart valves, intestines & bone

marrow


Conditions Affecting Tissue Repair

• Nutrition– adequate protein for structural components– vitamin C for production of collagen and new blood vessels

• Proper blood circulation– delivers O2 & nutrients & removes fluids & bacteria

• With aging– collagen fibers change in quality– elastin fibers fragment and abnormally bond to calcium– cell division and protein synthesis are slowed


DISORDERS: HOMEOSTATIC IMBALANCES

• Disorders of epithelial tissues are mainly specific to individual organs, such as skin cancer which involves the epidermis or peptic ulcer disease which involves the epithelial lining of the stomach or small intestine.

• The most prevalent disorders of connective tissue are autoimmune disorders which are diseases in which antibodies produced by the immune system fail to distinguish what is foreign from what is self and attacks the body’s own tissues.


Sjogren’s Syndrome

• Autoimmune disorder producing exocrine gland inflammation

• Dryness of mouth and eyes• 20 % of older adults show some signs


Systemic Lupus Erythematosus (SLE)

• Autoimmune disorder -- causes unknown• Chronic inflammation of connective tissue• Nonwhite women during childbearing years• Females 9:1 (1 in 2000 individuals)• Painful joints, ulcers, loss of hair, fever• Life-threatening if inflammation occurs in major organs

--- liver, kidney, heart, brain, etc.


end


Chapter 5

The Integumentary System

Lecture Outline


INTRODUCTION

• The skin and its accessory structures make up the integumentary system.

• The integumentary system functions to guard the body’s physical and biochemical integrity, maintain a constant body temperature, and provide sensory information about the surrounding environment.


Chapter 5The Integumentary System

• Skin and its accessory structures– structure– function– growth and repair– development– aging– disorders


General Anatomy

• A large organ composed of all 4 tissue types

• 22 square feet • 1-2 mm thick• Weight 10 lbs.


STRUCTURE OF THE SKIN (Figure 5.1)

• The superficial portion of the skin is the epidermis and is composed of epithelial tissue.

• The deeper layer of the skin is the dermis and is primarily composed of connective tissue.

• Deep to the dermis is the subcutaneous layer or hypodermis. (not a part of the skin)– It consists of areolar and adipose

tissue.– fat storage, an area for blood

vessel passage, and an area of pressure-sensing nerve endings.


Overview of Epidermis

• Stratified squamous epithelium– avascular (contains no blood vessels)– 4 types of cells– 5 distinct strata (layers) of cells


Four Principle Cells of the Epidermis – Figure 5.2

• keratinocytes (Figure 5.2a)

– produce the protein keratin, which helps protect the skin and underlying tissue from heat, microbes, and chemicals, and lamellar granules, which release a waterproof sealant

• melanocytes (Figure 5.2b)

– produce the pigment melanin which contributes to skin color and absorbs damaging ultraviolet (UV) light

• Langerhans cells (Figure 5.2c)

– derived from bone marrow

– participate in immune response

• Merkel cells (Figure 5.2d)

– contact a sensory structure called a tactile (Merkel) disc and function in the sensation of touch


Layers of the Epidermis

• There are four or five layers of the epidermis, depending upon the degree of friction and mechanical pressure applied to the skin.

• From deepest to most superficial the layers of the epidermis are (Figures 5.3 a and b).– stratum basale (stratum germinativum)– stratum spinosum– stratum granulosum– stratum lucidum (only in palms and soles)– stratum corneum


Layers (Strata) of the Epidermis• Stratum corneum• Stratum lucidum• Stratum granulosum• Stratum spinosum• Stratum basale


Stratum Basale (stratum germinativum)

• Deepest single layer of epidermis – merkel cells, melanocytes,

keratinocytes & stem cells that divide repeatedly

– keratinocytes have a cytoskeleton of tonofilaments

– Cells attached to each other & to basement membrane by desmosomes & hemi-desmosomes

• When the germinal portion of the epidermis is destroyed, new skin cannot regenerate with a skin graft.


Stratum Spinosum (Figure 5.2a)

• provides strength and flexibility to the skin

– 8 to 10 cell layers are held together by desmosomes.

– During slide preparation, cells shrink and appear spiny (where attached to other cells by desmosomes.)

• Melanin is taken in by keratinocytes (by phagocytosis) from nearby melanocytes.


Stratum Granulosum

• transition between the deeper, metabolically active strata and the dead cells of the more superficial strata

• 3-5 layers of flat dying cells that show nuclear degeneration– example of apoptosis

• Contain lamellar granules that release lipid that repels water

• Contain dark-staining keratohyalin granules– keratohyalin converts

tonofilaments into keratin


Stratum Lucidum

• present only in the fingers tips, palms of the hands, and soles of the feet.

• Three to five layers of clear, flat, dead cells

• Contains precursor of keratin


Stratum Corneum

• 25 to 30 layers of flat dead cells filled with keratin and surrounded by lipids– continuously shed

• Barrier to light, heat, water, chemicals & bacteria

• Lamellar granules in this layer make it water-repellent.

• Constant exposure to friction will cause this layer to increase in depth with the formation of a callus, an abnormal thickening of the epidermis.


Keratinization and Growth of the Epidermis

• Stem cells divide to produce keratinocytes• As keratinocytes are pushed up towards the surface, they fill

with keratin– Keratinization is replacement of cell contents with the

protein keratin; occurs as cells move to the skin surface over 2-4 weeks.

• Epidermal growth factor (EGF) and other hormone-like proteins play a role in epidermal growth.

• Table 5.1 presents a summary of the features of the epidermal strata.


Clinical Application

• Psoriasis is a chronic skin disorder characterized by a more rapid division and movement of keratinocytes through the epidermal strata .– cells shed in 7 to 10 days as flaky silvery scales– abnormal keratin produced

• Skin Grafts– New skin can not regenerate if stratum basale and its stem cells are

destroyed– autograft: covering of wound with piece of healthy skin from self– isograft is from twin– autologous skin

• transplantation of patient’s skin after it has grown in culture


Dermis (Figure 5.1)• Connective tissue layer composed of collagen & elastic

fibers, fibroblasts, macrophages & fat cells• Contains hair follicles, glands, nerves & blood vessels• Two major regions of dermis

– papillary region– reticular region


Dermis - Papillary Region

• Top 20% of dermis• areolar connective tissue containing fine elastic fibers, corpuscles of

touch (Meissner’s corpuscles), adipose cells, hair follicles, sebaceous glands, sudoriferous glands – The collagen and elastic fibers provide strength, extensibility (ability

to stretch), and elasticity (ability to return to original shape after stretching) to skin.

• Finger like projections are called dermal papillae– anchors epidermis to dermis– contains capillaries that feed epidermis– contains Meissner’s corpuscles (touch) & free nerve endings for

sensations of heat, cold, pain, tickle, and itch


Dermis - Reticular Region

• Dense irregular connective tissue• Contains interlacing collagen and elastic fibers• Packed with oil glands, sweat gland ducts, fat & hair follicles• Provides strength, extensibility & elasticity to skin

– stretch marks are dermal tears from extreme stretching• Epidermal ridges form in fetus as epidermis conforms to

dermal papillae– fingerprints are left by sweat glands open on ridges– increase grip of hand


Dermis -- Structure

• Epidermal ridges increase friction for better grasping ability and provide the basis for fingerprints and footprints. The ridges typically reflect contours of the underlying dermis.

• Lines of cleavage in the skin indicate the predominant direction of the underlying collagen fibers. Knowledge of these lines is especially important to plastic surgeons.

• Table 5.2 presents a comparison of the structural features of the papillary and reticular regions of the dermis.


Tattoos

• Tattooing is a permanent coloration of the skin in which a foreign pigment is injected into the dermis.


Basis of Skin Color

• The color of skin and mucous membranes can provide clues for diagnosing certain problems, such as – Jaundice

• yellowish color to skin and whites of eyes• buildup of yellow bilirubin in blood from liver disease

– Cyanosis• bluish color to nail beds and skin• hemoglobin depleted of oxygen looks purple-blue

– Erythema• redness of skin due to enlargement of capillaries in

dermis• during inflammation, infection, allergy or burns


Skin Color Pigments• Melanin produced in epidermis by melanocytes

– melanocytes convert tyrosine to melanin• UV in sunlight increases melanin production

– same number of melanocytes in everyone, but differing amounts of pigment produced

– results vary from yellow to tan to black color• Clinical observations

– freckles or liver spots = melanocytes in a patch– albinism = inherited lack of tyrosinase; no pigment– vitiligo = autoimmune loss of melanocytes in areas of the skin

produces white patches

• The wide variety of colors in skin is due to three pigments - melanin, carotene, and hemoglobin (in blood in capillaries) - in the dermis.


Skin Color Pigments

• Carotene in dermis– yellow-orange pigment (precursor of vitamin A)– found in stratum corneum & dermis

• Hemoglobin– red, oxygen-carrying pigment in blood cells– if other pigments are not present, epidermis is

translucent so pinkness will be evident


Accessory Structures of Skin

• develop from the embryonic epidermis

• Cells sink inward during development to form:– hair– oil glands– sweat glands– nails


HAIR

• Hairs, or pili, are present on most skin surfaces except the palms, palmar surfaces of the digits, soles, and plantar surfaces of the digits.

• Hair consists of – a shaft above the surface (Figure 5.5a)– a root that penetrates the dermis and

subcutaneous layer (Figure 5.5c,d)– the cuticle (Figure 5.5b), and – a hair follicle (Figure 5.5c,d).

• New hairs develop from cell division of the matrix in the bulb.


Structure of Hair

• Shaft -- visible– medulla, cortex & cuticle– CS round in straight hair– CS oval in wavy hair

• Root -- below the surface

• Follicle surrounds root– external root sheath– internal root sheath– base of follicle is bulb

• blood vessels• germinal cell layer


Structure of Hair






Structure of Hair






Hair Related Structures

• Arrector pili– smooth muscle in

dermis contracts with cold or fear.

– forms goosebumps as hair is pulled vertically

• Hair root plexus– detect hair movement

• sebaceous (oil) glands


Types of hair

• Lanugo is a fine, nonpigmented hair that covers the fetus.• Vellus hair is a short, fine hair that replaces lanugo• Course pigmented hair appears in response to androgens• Hair that appears in response to androgens and hair of the

head, eyelashes and eyebrows is known as terminal hair.


Hair removal

• Depilatories dissolve the protein in the hair shaft• Electrolysis uses an electric current to destroy the hair

matrix.


Hair Growth

• The hair growth cycle consists of a growing stage and a resting stage.– Growth cycle = growth stage & resting stage

• Growth stage – lasts for 2 to 6 years– matrix cells at base of hair root producing length

• Resting stage– lasts for 3 months– matrix cells inactive & follicle atrophies

– Old hair falls out as growth stage begins again• normal hair loss is 70 to 100 hairs per day

• Both rate of growth and the replacement cycle can be altered by illness, diet, high fever, surgery, blood loss, severe emotional stress, and gender.

• Chemotherapeutic agents affect the rapidly dividing matrix hair cells resulting in hair loss.


Hair Color

• Hair color is due primarily to the amount and type of melanin.

• Graying of hair occurs because of a progressive decline in tyrosinase.– Dark hair contains true melanin– Blond and red hair contain melanin with iron and sulfur

added– Graying hair is result of decline in melanin production– White hair has air bubbles in the medullary shaft

• Hormones influence the growth and loss of hair (Clinical applications).


Functions of Hair

• Prevents heat loss• Decreases sunburn• Eyelashes help protect eyes• Touch receptors (hair root

plexus) senses light touch


Glands of the Skin

• Specialized exocrine glands found in dermis

• Sebaceous (oil) glands• Sudiferous (sweat) glands• Ceruminous (wax) glands• Mammary (milk) glands


Sebaceous (oil) glands

• Sebaceous (oil) glands are usually connected to hair follicles; they are absent in the palms and soles (Figures 5.1 and 5.6a).

• Secretory portion of gland is located in the dermis– produce sebum

• contains cholesterol, proteins, fats & salts• moistens hairs• waterproofs and softens the skin• inhibits growth of bacteria & fungi (ringworm)

• Acne– bacterial inflammation of glands– secretions are stimulated by hormones at puberty


Sudoriferous (sweat) glandsEccrine sweat glands have an extensive distribution most areas of skin

– secretory portion is in dermis with duct to surface– ducts terminate at pores at the surface of the epidermis (Figure

5.6b).– regulate body temperature through evaporation (perspiration)– help eliminate wastes such as urea.

Apocrine sweat glands are limited in distribution to the skin of the axilla, pubis, and areolae; their duct open into hair follicles (Figure 5.6c).– secretory portion in dermis– duct that opens onto hair follicle– secretions are more viscous

• Table 5.3 compares eccrine and apocrine sweat glands.


Ceruminous Glands

• Ceruminous glands are modified sudoriferous glands that produce a waxy substance called cerumen. – found in the external auditory meatus– contains secretions of oil and wax glands– barrier for entrance of foreign bodies

• An abnormal amount of cerumen in the external auditory meatus or canal can result in impaction and prevent sound waves from reaching the ear drum (Clinical Application).


Structure of Nails (Figure 5.7)

• Tightly packed keratinized cells• Nail body

– visible portion pink due to underlying capillaries

– free edge appears white• Nail root

– buried under skin layers– lunula is white due to thickened

stratum basale• Eponychium (cuticle)

– stratum corneum layer


Nail Growth

• Nail matrix is below nail root -- produces growth

• Cells transformed into tightly packed keratinized cells

• 1 mm per week

• Certain nail conditions may indicate disease (Figure 5.8)


TYPES OF SKIN• Thin skin

– covers all parts of the body except for the palms and palmar surfaces of the digits and toes.

– lacks epidermal ridges– has a sparser distribution of sensory receptors than thick

skin.• Thick skin (0.6 to 4.5 mm)

– covers the palms, palmar surfaces of the digits, and soles

– features a stratum lucidum and thick epidermal ridges– lacks hair follicles, arrector pili muscles, and sebaceous

glands, and has more sweat glands than thin skin.• Table 5.4 summarizes the fractures of thin and thick skin.


FUNCTIONS OF SKIN -- thermoregulation• Perspiration & its evaporation

– lowers body temperature– flow of blood in the dermis is adjusted

• Exercise– in moderate exercise, more blood brought to surface

helps lower temperature– with extreme exercise, blood is shunted to muscles and

body temperature rises

• Shivering and constriction of surface vessels– raise internal body temperature as needed


FUNCTIONS OF SKIN• blood reservoir

– extensive network of blood vessels

• protection - physical, chemical and biological barriers– tight cell junctions prevent bacterial invasion– lipids released retard evaporation– pigment protects somewhat against UV light– Langerhans cells alert immune system

• cutaneous sensations – touch, pressure, vibration, tickle, heat, cold, and pain arise

in the skin


FUNCTIONS OF SKIN• Synthesis of Vitamin D

– activation of a precursor molecule in the skin by UV light– enzymes in the liver and kidneys modify the activated

molecule to produce calcitriol, the most active form of vitamin D.

– necessary vitamin for absorption of calcium from food in the gastrointestinal tract

• excretion– 400 mL of water/day, small amounts salt, CO2, ammonia

and urea


Transdermal Drug Administration

• method of drug passage across the epidermis and into the blood vessels of the dermis– drug absorption is most rapid in areas where skin is thin

(scrotum, face and scalp)• Examples:

– nitroglycerin (prevention of chest pain from coronary artery disease)

– scopolamine ( motion sickness)– estradiol (estrogen replacement therapy)– nicotine (stop smoking alternative)


MAINTAINING HOMEOSTASIS: SKIN WOUND HEALING


Epidermal Wound Healing• Abrasion or minor burn• Basal cells migrate across the wound (Figure 5.9a)• Contact inhibition with other cells stops migration• Epidermal growth factor stimulates basal cells to

divide and replace the ones that have moved into the wound (Figure 5.9b).

• Full thickness of epidermis results from further cell division


Deep Wound Healing• When an injury extends to tissues deep to the epidermis, the repair process is more complex than epidermal healing, and

scar formation results.

• Healing occurs in 4 phases

– inflammatory phase has clot unite wound edges and WBCs arrive from dilated and more permeable blood vessels

– migratory phase begins the regrowth of epithelial cells and the formation of scar tissue by the fibroblasts

– proliferative phase is a completion of tissue formation

– maturation phase sees the scab fall off

• Scar formation

– hypertrophic scar remains within the boundaries of the original wound

– keloid scar extends into previously normal tissue

• collagen fibers are very dense and fewer blood vessels are present so the tissue is lighter in color


Deep Wound Healing

• Phases of Deep Wound Healing– During the inflammatory phase, a blood clot unites the

wound edges, epithelial cells migrate across the wound, vasodilatation and increased permeability of blood vessels deliver phagocytes, and fibroblasts form (Figure 5.9c).

– During the migratory phase, epithelial cells beneath the scab bridge the wound, fibroblasts begin scar tissue, and damaged blood vessels begin to grow. During this phase, tissue filling the wound is called granulation tissue.


Phases of Deep Wound Healing


Deep Wound Healing

• Phases of Deep Wound Healing– During the proliferative phase, the events of the

migratory phase intensify.– During the maturation phase, the scab sloughs off, the

epidermis is restored to normal thickness, collagen fibers become more organized, fibroblasts begin to disappear, and blood vessels are restored to normal (Figure 5.9).

– Scar tissue formation (fibrosis) can occur in deep wound healing.


DEVELOPMENT OF THE INTEGUMENTARY SYSTEM

• Epidermis develops from ectodermal germ layer– Hair, nails, and skin glands are epidermal derivatives

(Figure 5.10a).– The connective tissue and blood vessels associated with

the gland develop from mesoderm.• Dermis develops from mesenchymal mesodermal germ

layer cells


Development of the Skin

• Timing– at 8 weeks, fetal “skin” is

simple cuboidal– nails begin to form at 10

weeks, but do not reach the fingertip until the 9th month

– dermis forms from mesoderm by 11 weeks

– by 16 weeks, all layers of the epidermis are present

– oil and sweat glands form in 4th and 5th month

– by 6th months, delicate fetal hair (lanugo) has formed

• Slippery coating of oil and sloughed off skin called vernix caseosa is present at birth


Age Related Structural Changes

• Collagen fibers decrease in number & stiffen • Elastic fibers become less elastic• Fibroblasts decrease in number• decrease in number of melanocytes (gray hair, blotching)• decrease in Langerhans cells (decreased immune

responsiveness)• reduced number and less-efficient phagocytes


AGING AND THE INTEGUMENTARY SYSTEM

• Most of the changes occur in the dermis– wrinkling, slower growth of hair and nails– dryness and cracking due to sebaceous gland atrophy– Walls of blood vessels in dermis thicken so decreased

nutrient availability leads to thinner skin as subcutaneous fat is lost.

• anti-aging treatments– microdermabrasion, chemical peel, laser resurfacing,

dermal fillers, Botuliism toxin injection, and non surgical face lifts.

– Sun screens and sun blocks help to minimize photodamage from ultraviolet exposure


Photodamage

• Ultraviolet light (UVA and UVB) both damage the skin• Acute overexposure causes sunburn• DNA damage in epidermal cells can lead to skin cancer• UVA produces oxygen free radicals that damage collagen

and elastic fibers and lead to wrinkling of the skin


DISORDERS: HOMEOSTATIC IMBALANCES

• Skin cancer can be caused by excessive exposure to sunlight.

• Among the risk factors for skin cancer are skin type, sun exposure, family history, age, and immunologic status.– The three most common forms are – basal cell carcinoma, – squamous cell carcinoma, and – malignant melanoma.


Skin Cancer• 1 million cases diagnosed per year• 3 common forms of skin cancer

– basal cell carcinoma (rarely metastasize)– squamous cell carcinoma (may metastasize)– malignant melanomas (metastasize rapidly)

• most common cancer in young women• arise from melanocytes ----life threatening• key to treatment is early detection watch for

changes in symmetry, border, color and size• risks factors include-- skin color, sun exposure,

family history, age and immunological status


Burns

• Tissue damage from excessive heat, electricity, radioactivity, or corrosive chemicals that destroys (denatures) proteins in the exposed cells is called a burn.

• Generally, the systemic effects of a burn are a greater threat to life than are the local effects.

• The seriousness of a burn is determined by its depth, extent, and area involved, as well as the person’s age and general health. When the burn area exceeds 70%, over half of the victims die.


Burns

• Destruction of proteins of the skin– chemicals, electricity, heat

• Problems that result– shock due to water, plasma and plasma protein

loss– circulatory & kidney problems from loss of

plasma– bacterial infection

• Two methods for determining the extent of a burn are the rule of nines and the Lund-Bowder method (Figure 5.13).


Burns


Types of Burns

• First-degree– only epidermis (sunburn)

• Second-degree burn – destroys entire epidermis & part of dermis – fluid-filled blisters separate epidermis & dermis– epidermal derivatives are not damaged– heals without grafting in 3 to 4 weeks & may scar

• Third-degree or full-thickness– destroy epidermis, dermis & epidermal derivatives– damaged area is numb due to loss of sensory nerves


Burns


Pressure Sores

• Pressure ulcers, also known as decubitus ulcers– caused by a constant deficiency of blood to

tissues overlying a bony projection that has been subjected to prolonged pressure

– typically occur between bony projection and hard object such as a bed, cast, or splint

– the deficiency of blood flow results in tissue ulceration.

• Preventable with proper care


end


Chapter 6

The Skeletal System: Bone Tissue

Lecture Outline


INTRODUCTION

• Bone is made up of several different tissues working together: bone, cartilage, dense connective tissue, epithelium, various blood forming tissues, adipose tissue, and nervous tissue.

• Each individual bone is an organ; the bones, along with their cartilages, make up the skeletal system.


Chapter 6The Skeletal System:Bone Tissue

• Dynamic and ever-changing throughout life• Skeleton composed of many different tissues

– cartilage, bone tissue, epithelium, nerve, blood forming tissue, adipose, and dense connective tissue


Functions of Bone

• Supporting & protecting soft tissues• Attachment site for muscles making movement

possible• Storage of the minerals, calcium & phosphate --

mineral homeostasis • Blood cell production occurs in red bone

marrow (hemopoiesis)• Energy storage in yellow bone marrow


Anatomy of a Long Bone

• diaphysis = shaft• epiphysis = one end of a

long bone• metaphyses are the

areas between the epiphysis and diaphysis and include the epiphyseal plate in growing bones.

• Articular cartilage over joint surfaces acts as friction reducer & shock absorber

• Medullary cavity = marrow cavity


Anatomy of a Long Bone

• Endosteum = lining of marrow cavity

• Periosteum = tough membrane covering bone but not the cartilage – fibrous layer = dense

irregular CT– osteogenic layer =

bone cells & blood vessels that nourish or help with repairs


Histology of Bone

• A type of connective tissue as seen by widely spaced cells separated by matrix

• Matrix of 25% water, 25% collagen fibers & 50% crystalized mineral salts

• 4 types of cells in bone tissue


HISTOLOGY OF BONE TISSUE

• Bone (osseous) tissue consists of widely separated cells surrounded by large amounts of matrix.

• The matrix of bone contains inorganic salts, primarily hydroxyapatite and some calcium carbonate, and collagen fibers.

• These and a few other salts are deposited in a framework of collagen fibers, a process called calcification or mineralization.– The process of calcification occurs only in the presence

of collagen fibers.– Mineral salts confer hardness on bone while collagen

fibers give bone its great tensile strength.


bone cells.(Figure 6.2)

1. Osteogenic cells undergo cell division and develop into osteoblasts.

2. Osteoblasts are bone-building cells.

3. Osteocytes are mature bone cells and the principal cells of bone tissue.

4. Osteoclasts are derived from monocytes and serve to break down bone tissue.


Cells of Bone

• Osteoprogenitor cells ---- undifferentiated cells – can divide to replace themselves & can become osteoblasts– found in inner layer of periosteum and endosteum

• Osteoblasts--form matrix & collagen fibers but can’t divide• Osteocytes ---mature cells that no longer secrete matrix• Osteoclasts---- huge cells from fused monocytes (WBC)

– function in bone resorption at surfaces such as endosteum


Cells of Bone

Osteoblasts Osteocytes Osteoclasts


Matrix of Bone

• Inorganic mineral salts provide bone’s hardness– hydroxyapatite (calcium phosphate) & calcium carbonate

• Organic collagen fibers provide bone’s flexibility– their tensile strength resists being stretched or torn– remove minerals with acid & rubbery structure results

• Bone is not completely solid since it has small spaces for vessels and red bone marrow– spongy bone has many such spaces– compact bone has very few such spaces


Compact Bone

• Compact bone is arranged in units called osteons or Haversian systems (Figure 6.3a).

• Osteons contain blood vessels, lymphatic vessels, nerves, and osteocytes along with the calcified matrix.

• Osteons are aligned in the same direction along lines of stress. These lines can slowly change as the stresses on the bone changes.


Compact or Dense Bone

• Looks like solid hard layer of bone• Makes up the shaft of long bones and the external layer

of all bones • Resists stresses produced by weight and movement


Histology of Compact Bone

• Osteon is concentric rings (lamellae) of calcified matrix surrounding a vertically oriented blood vessel

• Osteocytes are found in spaces called lacunae• Osteocytes communicate through canaliculi filled with

extracellular fluid that connect one cell to the next cell• Interstitial lamellae represent older osteons that have been

partially removed during tissue remodeling


Spongy Bone

• Spongy (cancellous) bone does not contain osteons. It consists of trabeculae surrounding many red marrow filled spaces (Figure 6.3b).

• It forms most of the structure of short, flat, and irregular bones, and the epiphyses of long bones.

• Spongy bone tissue is light and supports and protects the red bone marrow.


The Trabeculae of Spongy Bone

• Latticework of thin plates of bone called trabeculae oriented along lines of stress

• Spaces in between these struts are filled with red marrow where blood cells develop

• Found in ends of long bones and inside flat bones such as the hipbones, sternum, sides of skull, and ribs.

No true Osteons.


Blood and Nerve Supply of Bone

• Periosteal arteries– supply periosteum

• Nutrient arteries– enter through nutrient

foramen– supplies compact bone of

diaphysis & red marrow• Metaphyseal & epiphyseal aa.

– supply red marrow & bone tissue of epiphyses


BONE FORMATION

• All embryonic connective tissue begins as mesenchyme.• Bone formation is termed osteogenesis or ossification and

begins when mesenchymal cells provide the template for subsequent ossification.

• Two types of ossification occur.– Intramembranous ossification is the formation of bone

directly from or within fibrous connective tissue membranes.

– Endochondrial ossification is the formation of bone from hyaline cartilage models.


Intramembranous

• Intramembranous ossification forms the flat bones of the skull and the mandible (Figure 6.5).– An ossification center forms from mesenchymal cells as

they convert to osteoblasts and lay down osteoid matrix.– The matrix surrounds the cell and then calcifies as the

osteoblast becomes an osteocyte.– The calcifying matrix centers join to form bridges of

trabeculae that constitute spongy bone with red marrow between.

– On the periphery the mesenchyme condenses and develops into the periosteum.


Intramembranous Bone Formation

• Mesenchymal cells become osteoprogenitor cells then osteoblasts.

• Osteoblasts surround themselves with matrix to become osteocytes.


Intramembranous Bone Formation (cont.)

• Matrix calcifies into trabeculae with spaces holding red bone marrow.

• Mesenchyme condenses as periosteum at the bone surface.

• Superficial layers of spongy bone are replaced with compact bone.


Intramembranous Bone Formation


Endochondrial

• Endochondrial ossification involves replacement of cartilage by bone and forms most of the bones of the body (Figure 6.6).

• The first step in endochondrial ossification is the development of the cartilage model.


Endochondral Bone Formation

• Development of Cartilage model– Mesenchymal cells form a

cartilage model of the bone during development

• Growth of Cartilage model– in length by chondrocyte cell

division and matrix formation ( interstitial growth)

– in width by formation of new matrix on the periphery by new chondroblasts from the perichondrium (appositional growth)

– cells in midregion burst and change pH triggering calcification and chondrocyte death



• Development of Primary Ossification Center– perichondrium lays down

periosteal bone collar– nutrient artery penetrates

center of cartilage model– periosteal bud brings

osteoblasts and osteoclasts to center of cartilage model

– osteoblasts deposit bone matrix over calcified cartilage forming spongy bone trabeculae

– osteoclasts form medullary cavity



• Development of Secondary Ossification Center– blood vessels enter the epiphyses around time of birth– spongy bone is formed but no medullary cavity

• Formation of Articular Cartilage– cartilage on ends of bone remains as articular cartilage.


Bone Scan

• Radioactive tracer is given intravenously• Amount of uptake is related to amount of blood flow to

the bone• “Hot spots” are areas of increased metabolic activity that

may indicate cancer, abnormal healing or growth• “Cold spots” indicate decreased metabolism of

decalcified bone, fracture or bone infection


BONE GROWTH


Growth in Length

• To understand how a bone grows in length, one needs to know details of the epiphyseal or growth plate (Figure 6.7).

• The epiphyseal plate consists of four zones: (Figure 6.7b)– zone of resting cartilage, – zone of proliferation cartilage, – zone of hypertrophic cartilage, and – zone of calcified cartilage The activity of the epiphyseal

plate is the only means by which the diaphysis can increase in length.

• When the epiphyseal plate closes, is replaced by bone, the epiphyseal line appears and indicates the bone has completed its growth in length.


Bone Growth in Length

• Epiphyseal plate or cartilage growth plate– cartilage cells are produced by

mitosis on epiphyseal side of plate– cartilage cells are destroyed and

replaced by bone on diaphyseal side of plate

• Between ages 18 to 25, epiphyseal plates close.– cartilage cells stop dividing and

bone replaces the cartilage (epiphyseal line)

• Growth in length stops at age 25


Zones of Growth in Epiphyseal Plate

• Zone of resting cartilage – anchors growth plate to bone

• Zone of proliferating cartilage– rapid cell division (stacked coins)

• Zone of hypertrophic cartilage– cells enlarged & remain in

columns• Zone of calcified cartilage

– thin zone, cells mostly dead since matrix calcified

– osteoclasts removing matrix– osteoblasts & capillaries move in

to create bone over calcified cartilage


Growth in Thickness

• Bone can grow in thickness or diameter only by appositional growth (Figure 6.8).

• The steps in thes process are:– Periosteal cells differentiate into osteoblasts which

secrete collagen fibers and organic molecules to form the matrix.

– Ridges fuse and the periosteum becomes the endosteum.

– New concentric lamellae are formed.– Osetoblasts under the peritsteum form new

circumferential lamellae.


Bone Growth in Width

• Only by appositional growth at the bone’s surface• Periosteal cells differentiate into osteoblasts and form bony ridges and

then a tunnel around periosteal blood vessel.• Concentric lamellae fill in the tunnel to form an osteon.


Factors Affecting Bone Growth

• Nutrition– adequate levels of minerals and vitamins

• calcium and phosphorus for bone growth• vitamin C for collagen formation• vitamins K and B12 for protein synthesis

• Sufficient levels of specific hormones– during childhood need insulinlike growth factor

• promotes cell division at epiphyseal plate• need hGH (growth), thyroid (T3 &T4) and insulin

– sex steroids at puberty– At puberty the sex hormones, estrogen and testosterone,

stimulate sudden growth and modifications of the skeleton to create the male and female forms.


Hormonal Abnormalities

• Oversecretion of hGH during childhood produces giantism• Undersecretion of hGH or thyroid hormone during childhood

produces short stature• Both men or women that lack estrogen receptors on cells

grow taller than normal– estrogen is responsible for closure of growth plate


BONES AND HOMEOSTASIS


Bone Remodeling

• Remodeling is the ongoing replacement of old bone tissue by new bone tissue.– Old bone is constantly destroyed by osteoclasts, whereas

new bone is constructed by osteoblasts.– In orthodontics teeth are moved by brraces. This places

stress on bone in the sockets causing osteoclasts and osteablasts to remodel the sockets so that the teeth can be properly aligned (Figure 6.2)

– Several hormones and calcitrol control bone growth and bone remodeling (Figure 6.11)


Bone Remodeling

• Ongoing since osteoclasts carve out small tunnels and osteoblasts rebuild osteons.– osteoclasts form leak-proof seal around cell edges– secrete enzymes and acids beneath themselves– release calcium and phosphorus into interstitial fluid– osteoblasts take over bone rebuilding

• Continual redistribution of bone matrix along lines of mechanical stress – distal femur is fully remodeled every 4 months


Fracture and Repair of Bone

A fracture is any break in a bone.• Fracture repair (Figure 6.10)involves formation of a clot

called a fracture hematoma, organization of the fracture hematoma into granulation tissue called a procallus (subsequently transformed into a fibrocartilaginous [soft] callus), conversion of the fibrocartilaginous callus into the spongy bone of a bony (hard) callus, and, finally, remodeling of the callus to nearly original form.


Fracture & Repair of Bone

• Healing is faster in bone than in cartilage due to lack of blood vessels in cartilage

• Healing of bone is still slow process due to vessel damage

• Clinical treatment– closed reduction = restore

pieces to normal position by manipulation

– open reduction = realignment during surgery


Fractures

• Named for shape or position of fracture line• Common types of fracture

– greenstick -- partial fracture– impacted -- one side of fracture driven into the interior

of other side


Fractures


– closed -- no break in skin– open fracture --skin broken– comminuted -- broken ends of bones are

fragmented


Fractures


– Pott’s -- distal fibular fracture– Colles’s -- distal radial fracture– stress fracture -- microscopic fissures from

repeated strenuous activities


Repair of a Fracture



• Formation of fracture hematoma– damaged blood vessels produce clot in 6-8 hours, bone cells die– inflammation brings in phagocytic cells for clean-up duty– new capillaries grow into damaged area

• Formation of fibrocartilagenous callus formation– fibroblasts invade the procallus & lay down collagen fibers– chondroblasts produce fibrocartilage to span the broken ends of the bone



• Formation of bony callus– osteoblasts secrete spongy bone that joins 2 broken ends of

bone– lasts 3-4 months

• Bone remodeling– compact bone replaces the spongy in the bony callus– surface is remodeled back to normal shape


Calcium Homeostasis & Bone Tissue

• Skeleton is a reservoir of Calcium & Phosphate• Calcium ions involved with many body systems

– nerve & muscle cell function– blood clotting– enzyme function in many biochemical reactions

• Small changes in blood levels of Ca+2 can be deadly (plasma level maintained 9-11mg/100mL)– cardiac arrest if too high– respiratory arrest if too low


Hormonal Influences

• Parathyroid hormone (PTH) is secreted if Ca+2 levels falls– PTH gene is turned on & more PTH is

secreted from gland– osteoclast activity increased, kidney

retains Ca+2 and produces calcitriol• Calcitonin hormone is secreted from

parafollicular cells in thyroid if Ca+2 blood levels get too high– inhibits osteoclast activity– increases bone formation by

osteoblasts


EXERCISE AND BONE TISSUE

• Within limits, bone has the ability to alter its strength in response to mechanical stress by increasing deposition of mineral salts and production of collagen fibers.– Removal of mechanical stress leads to weakening of

bone through demineralization (loss of bone minerals) and collagen reduction.

• reduced activity while in a cast• astronauts in weightless environment• bedridden person

– Weight-bearing activities, such as walking or moderate weightlifting, help build and retain bone mass.


Development of Bone Tissue

• Both types of bone formation begin with mesenchymal cells

• Mesenchymal cells transform into chondroblasts which form cartilage

OR

• Mesenchymal cells become osteoblasts which form bone

Mesenchymal Cells


Developmental Anatomy

5th Week =limb bud appears as mesoderm covered with ectoderm

6th Week = constriction produces hand or foot plate

and skeleton now totally cartilaginous

7th Week = endochondral ossification begins

8th Week = upper & lower limbs appropriately named


AGING AND BONE TISSUE

• Of two principal effects of aging on bone, the first is the loss of calcium and other minerals from bone matrix (demineralization), which may result in osteoporosis.– very rapid in women 40-45 as estrogens levels decrease – in males, begins after age 60

• The second principal effect of aging on the skeletal system is a decreased rate of protein synthesis– decrease in collagen production which gives bone its

tensile strength– decrease in growth hormone– bone becomes brittle & susceptible to fracture


Osteoporosis

• Decreased bone mass resulting in porous bones • Those at risk

– white, thin menopausal, smoking, drinking female with family history

– athletes who are not menstruating due to decreased body fat & decreased estrogen levels

– people allergic to milk or with eating disorders whose intake of calcium is too low

• Prevention or decrease in severity– adequate diet, weight-bearing exercise, & estrogen

replacement therapy (for menopausal women)– behavior when young may be most important factor


Disorders of Bone Ossification

• Rickets• calcium salts are not deposited properly• bones of growing children are soft• bowed legs, skull, rib cage, and pelvic deformities

result• Osteomalacia

• new adult bone produced during remodeling fails to ossify

• hip fractures are common


end

Documents

Principles of Human Anatomy and Physiology, 11e1 Chapter 4 The Tissue Level of Organization Lecture Outline